This invention relates to flexible intermediate bulk containers (FIBC) used in the storage and transport of bulk products in granular, powder or paste forms.
Such FIBCs having integral lifting means, i.e. the lifting means are extensions of the side wall structure. The total width of all lifting means constitutes at least 25 % of the FIBC circumference, and at least 50 % of the longitudinal fibers of the wall structure are directly employed when the FIBC is lifted.
Generally speaking FIBCs are manufactured from at least one piece of woven fabric, particularly woven poly-propylene or other suitable synthetic material and are required to carry loads of 500 or more with a considerable safety margin.
Several proposals for the construction of such FIBCs are known. Typical common features are:
a side wall structure made together from one or more panels of woven fabric stitched together to form a tube or from a piece of tubular fabric to thus eliminate side seams; PA0 a base construction closing the lower side wall structure; open end of the FIBC PA0 lifting mean(s) at the upper end of the side wall structure capable of taking the load when the lifting mean(s) are engaged with suitable lifting mechanisms such as hooks or tines of a fork lift truck; PA0 and frequently closing means at the upper end of the side wall structure in the form of a lid of flexible product, stitched to the upper circumference of the wall structure. The lid can be equipped with a filling spout of flexible material. PA0 a. The horizontal load component, viewed perpendicular to the wall panels, results in hoop stress, since each part of the load from each lifting loop is not at the center of the wall panel. Thus, the longer the lifting loops, the smaller is the angle and the smaller will be the hoop stress component. PA0 b. A purely geometrical problem, due to the width of the lifting loop, which can be up to 1/4 of the FIBC circumference. In a FIBC according to above EP patent the extension of one wall panel is split in two halves, each to form a lifting loop and half of an adjacent wall panel. The edge of a lifting loop reaching from the top center of a wall panel to the top center of an adjacent wall panel will then have a shorter lifting height than the other edge of the lifting loop, which reaches to and from the upper corner between the two wall panels. The inner edge of the lifting loop will therefore take the higher load when the FIBC is lifted by fork lift truck tines.
The lifting means can be separate lifting loops stitched on to the side wall structure or be formed by integral extensions of the side wall structure.
In GB Pat. No. 1,475,019 the combined width of two lifting loops corresponds to 50 % of the FIBC circumference, i.e. all longitudinal fibers of the wall structure are employed when it is lifted.
FIBCs in accordance with above patent have proved to be very successful for the storage and transport of numerous bulk products. A major reason for such success has been the simple construction and the high lifting capacity of such FIBC's. However, the use of such FIBCs have also had their restrictions, especially when applied in areas with restricted overhead clearance, e.g. loading in closed containers or railway wagons, as the total height of such FIBC when lifted is too large compared with the fill height of the contained product.
For FIBCs having four lifting loops sewn onto the wall structure, restricted overhead clearance does not constitute a problem.
FIBCs having the tunnel shaped lifting loops, sewn on or integral with the wall structure, are also known.
From GB Patent No. 1,549,448 a FIBC having two tunnel shaped lifting loops, which are sewn onto two adjacent sides of a wall structure employing only 50 % of the longitudinal fibers of the wall structure when the FIBC is lifted, is known.
Further it is known from U.S. Pat. No. 4,300,608 to use two lifting loops which are integral parts of two opposing sides of the wall structure, again only 50 % of the side wall structure circumference being employed when the FIBC is lifted. In this respect these two known arrangements are identical. The latter, however, has the advantage of upraised and opened lifting loops due to the inserts of the lifting loops, thus making engagement with suitable lifting mechanisms, especially the tines of a fork lift truck, easy. As the inserts are separate pieces, this solution will be more expensive.
EP Pat. No. 0,050,845 relates to a FIBC manufactured from two or four panels of woven fabric which, when stitched together, form a FIBC with a single or double layer base and four integral lifting loops. The lifting loops are direct extensions of the panels constituting the wall structure and their combined width corresponds to 50 % of the circumference of the FIBC. Thus, all longitudinal fibers are employed when the FIBC is lifted.
FIBCs according to above EP-patent permits handling in areas with restricted overhead clearance, but the lifting capacity is reduced due to hoop stress concentrations at the top center of each of the four wall panels. Another disadvantage of these FIBCs is the apparent distortion of the lifting loops, thus making direct engagement with normal lifting mechanisms difficult. For example, a fork lift truck driver will need a helper to engage the tines of the fork lift truck into the lifting loops, thus increasing the cost of every handling operation. Both disadvantages can to some extent be reduced by increasing the length of the lifting loops, but then the requirement for overhead clearance increases. This type of FIBC constitutes an obvious compromise and its use will therefore be restricted.
In the continued research and development relating to this type of FIBCs, i.e. FIBCs having low lifting heights and a plurality of integral lifting loops, the inventors tried to meet the needs for improved lifting capacity, reliability and ease of handling.